Radio system



Aug. 16, 1927.

w. c. MacFApDEN RADIOSYSTEiK Filed Jan, 14. 1924 Patented Aug.'1-6, 1927.

UNITED STATES v 1,639,042 PATENT OFFICE.

WILFORD c. macrannnn, or PHILAD LPHIA, ranusrnvama, Assreuon. "r AT- wa'ran xnn'r manuracrunme com an or rnrnannnrnu, rnuxsnvnru, A ooaronarron or PENNSYLVANIA.

nan'ro swarm.

Application filed January 14, 1924, Serial No. 886,056.

My invention relates to radio systems, and more particularly to a system for receiving radio telegraphic or telephonic signals or .messages.

In accordance with my invention the received signal-or messagerepresenting energy is amplified, at radio frequency, in advance of detection or demodulation, in one or more stages each comprising a radio frequency amplifying tube or thermionic device whose input circuit is tuned and in whose anode circuit is the primary of a radio frequency transformer whose secondary is tuned and loosely coupled to and. relatively reversed with respect to the primary, in combination with loss producing means for maintaining the amplifier stable notwithstanding tuning of the input and secondary circuits throughout a wave length range for. which the anode circuit of the amplifier is aperiodlc and for which the amplifier is unstablewhen the inputand secondary circuits are tuned.

My invention resides in a system and apdegree of incandescence' or electron-emis sivity. Connected across the terminals of the battery A is the potentiometer resistance R, along wh1ch is movable. the contact 12 connected to one terminal of the secondary S and condenser C. In the anode circuit of each of the tubes V is a primary P of a radio frequency transformer and the anode circuit paratus of the character hereinafter described and claimed." I

For an illustration of one of the various forms m invention may take, reference is to be""ha td-the' accompanying drawing, in

which: 0

0 Fig. 1 is a diagrammatic view of a radio receiving system embodying my invention.

Fig. 2 is'illustrative of the relatlons of the transformer windings. I

Fig. 3 is a fragmentary diagrammatlc view illustrating a modification.

Referring toFig. 1,-theradiant energy absorbing structure comprises an antenna or equivalent absorbing structure D and the counter-capacity or earth connection E, be-

40 tween which is included the primary P of a radio frequency transformer. It will be understood, however, that other types of energy absorbing structure or circuits may be employed, including looped antennae or socalled frame aerials.

Inductively related to the primary P is the secondary S, in shunt with which is con nected the variable tuning condenser C for effecting tuning in the input circuit of the thermionic device V, of the so-called audion type comprising anode a, grid or control electrode g, and cathode or filament f. The tube V is utilized as a radio frequency amplifier of which there may be but one stage,

source or battery B, whose positive terminal is connected with one terminal of each of the last named primaries P, and whose other or negative terminal connects withthe negative terminal of the battery A and with each of the cathodes f. A condenser K, which -ma be of large fixed capacity, serves as a ra io frequency by-pass around the bat ary winding S,

tery B. Inductively related to each, of the last named primaries P is a transformer secondsame direction as t e primary P when viewed from the same end, and shunted by a variable tuning condenser C. The grids of the second tube V and the detector tube V are connected referably wound in the Y to one terminal of the last named secondaries S and condensers C, respectively, and the other terminals of these last named pairs of secondaries S and condensers C are connected by conductor 0 to the potentiometer contact 6, which 'is similarly connected with one'terminal of the secondary S and condenser C in the input circuit of the first tube-V. Ac-

I wave length of the order of condenser K being of large fixed capacity and exhibiting very small reactance at radio frequency. Through the conductor 0 and the connection d one terminal of each of the groups of secondaries S and condensers C in the input circuits of the several tubes is connected to earth or counter-capacity E.

In the gridv circuit of the detector or demodulator V is connected the usual grid condenser C shunted by a leak resistance B In the anode circuit of the tube V between the terminals e and it, may be connected a telephone instrument or the primary of an audio frequency transformer whose secondary is connected to the input circuit of an audio frequency amplifying tube. In the example illustrated a portion only of the battery B is utilized in the anode circuit of the tube V.

Aswell un erstood in the art, theaction in general of t e apparatus described is such as to amplify by each of the tubes V the radio frequency current representative of the received signal or message, while the tube V operates to amplify and detect or de-modulate, to produce in its anode circuit an audio frequency current representative of the signal and more particularly representing sound waves or speech.

To efiect stability of each of the radio frequency amplifiers V, that is, to prevent regenerative action or condition in which instability arises or oscillations are produced, the primary P in the anode circuit has so few turns, or, in general, exhibits such small inductance that with the associated capacity or capacities, and particularly the capacity between electrodes, as anode and grid, within the tube V, the anode circuit, by itself and irrespective of the tunable circuit coupled thereto, is aperiodic; that is, the anode circuit, unaffected by the tunable secondary circuit coupled thereto, is not in resonance or in tune with the radio frequency of the received energy for and throughout a predetermined range of frequencies or wave lengths of the'received energy. For example, the natural period of the anode circuit of each of the tubes V as determined or affected by'the inductance of the primary P is that corres onding with a 25 meters, with the result that the tube V will be'stable, in the sense that its anode circuit, when unaffected by the tuned secondary circuit coupled the eto, is aperiodic for wave lengths material y greater than seventy-five meters, preventing regenerative or feed-back action or the production ofsustained oscillations which, if occurring, disturb and interfere with satisfactory reception.

For the example given, the number of turns of the primary P may be about fifteen, the associated secondary S having about fifty-five or sixty turns, the ratio of tra 1 1sformation therefore being of the order of four, though somewhat smaller and considerably greater ratios of transformation may be utilized, depending on the degree of coupling.

The windings of a transformer of this character are indicated in Fig. 2, the primary P being disposed within the secondary S, and sufliciently spaced therefrom to prevent close coupling and to effect suitable looseness of coupling, whereby the tuning effect of the condenser C in shunt to the secondary S will have influence upon the anode may be wound on a cylindrical tube or member of insulating material having a diameter of 2 inches, while the secondaryS may be wound upon. a form or tube of molded insulating material, as bakelite, three inches in diameter, whereby the primary and secondary coils are spaced from each other about three-sixteenths 'of an inch, the difference in their diameters being about threeeighths of aninch.

The inductance of the primary P in the foregoing example is of the order .of 30 microhenries, that of the secondary S is'of the order of- 220 microhenries, and the mutual inductance, representative of the degree of coupling is of the order of about 50 microhenries only.

A transformer of the design above given by way of example will serve for radio fre-- quency amplifying purposes for wave lengths of the order of 450 meters to wave lengths of the order of 625 meters, when the secondary is tuned to those wave lengths, the

number of turns and inductance of the primary P being small, as stated, but suflicient,

however, to effectually transfer energy to its associated secondary for wave lengths of the order of 625 meters, there being an upper limit of the wave length utilizable, for with l increasing wave length the number of primary turns should increase to effectively.

transfer energy to the 'secdnda circuit. Tuning. the secondary circuit coup ed to the anode or primary circuit has the eflfect to render the-tube or amplifier V unstable, because tuning the secondary circuit has a tun;-

ing effect upon the anode or primary circuit which tends to make the tube unstable in the example given, however, when tuning to 450 m te s we upward y were 0? a varia l condenser, solely, as indicated, that is, without varying the inductance of the Secondary circuit, the increase in the capacity necessary for tuning is itself a stabilizing factor.

For wave lengths shorter than those of the order of 450 meters, down to wave lengths of the order of 250 meters, a transformer of the the potentiometer R may be provided,

whereby the grids of the several tubes are maintained at suitable potential higher or more positive than the most negative portion of their cathodes or filaments 7, thereby introducing vlosses by the resistance so introduced into the input circuit, and thereby suppressing regenerative act-ion or tendency to oscillations suitable, for example, for theadditional wave length range from about450 meters down to about 250 meters, the shortest wave length of the entire range and of the supplementary or additional range being, however, substantially longer than the wave length, for example, about 75 meters, for which the anode circuits by themselves become resonant or substantially so in virtue of primary continuously adjustable.

' stable when all the the relatively low inductance of the transformer primaries P connected therein.

In lieu of utilizing a potentiometer for the aforesaid purpose, each of the primaries P, in the anode circuits of the tubes V, may be made adjustable, as indicated in Fig. 3, either by taking out a suitable number of suitably spaced connecting taps, or by rendering the In such case the primary P will remain the same as before as to total number of turns, and the effect of the adjustment is'therefore to reduce the number of primary turns, thereby rendering the anode, circuit resonant for shorter and shorterwave lengths. By so adjusting the primary P, as, forexample, for

wave lengths shorter than of the order of 450 meters, the stable condition as effected by the primary P alone extends into lower wave length ranges, thereby preventing instability or oscillatory condition of a tube V for wave lengths lower than of the order of 450 meters, down to which wave length the tube V is turns of the primary P are in circuit. i 4

Or, in addition-to the utilization of a primary adjustable as toits number of turns as above. described, a potentiometer, as B", may be used, thereby further ensuring stability or effecting stability over a still Wider Wave length range additional or supplementary to the principal wave length range for which the adjustable primary P by itself ensures stability.

The transformer whose primary P is in the antenna path may be of the structure and .design'above described with respect to the tube coupling transformers. By so doing, the number of tuning adjustments is reduced to the numberof adjustments corresponding with the number of tuning condensers C. It serves also as a matter'of convenience in the matter of manufacture, in that all the radio frequency transformers are alike. However,

the primary P will render the antenna path or circuit resonant only for a particular wave length or narrow range of wavelengths, and

to this extent there is some sacrifice. However, it will be understood that the antenna path may be tuned, if desired, by adding thereto either an adjustable inductance or adjustable capacity, or both.

By recourse to the stabilizing means hereinbefore described,-the number of radio frequency amplifier stages utilizable is increased, and three, four or more stages of radio frequency amplification may be resorted to without instability, since each stage is rendered stable and the coupling between stages is loose, or in anyzevent not sufliciently close to efl'ect interaction through a series of stages to produce instability.

While I have described my invention with respect more particularly to short waves,

such as now commonly used in broadcast reception, it will be understood that the principles of my invention are applicable also to systems for 'aeceivin'g waves much longer than of the order of 600 or 625 meters, in or of wavelength ranges whose shortest wave length is much longer than of the order of 450 meters of the example hereinbefore given.

The stability of the tubes v and their associated-input and output circuits is ensured for wave lengths of about 450 meters described characteristics, whether or not. the

tubes and' the auxiliary apparatus and con- 'nections are assembled closely, as in a receiving unit -or set. When not so closely.

assembled in a. compact set, the stability is ensured, by recourse to transformers having the aforesaid characteristics, for an additional or supplemental wave length band or But when v assembled in a compactings P and S, these windings are so related,

as indicated in the drawing, that the high potential end of one is adjacent the low potential end of the other. In the example illustrated, that end of the primary P whose terminal connects with the anode is disposed adjacent that .end of the secondary S which is simultaneously at low potential. In other words, the primary P is connected in the reverse sense in the anode circuit to the sense in which the secondary S is connected in its circuit.

What I claim is:

1. A tuned radio frequency amplifier system comprising a three-electrode thermionic amplifier, means for tuning the input circuit thereof, a radio frequency transformer having its primaryin the anode circuit of said amplifier, the secondary of said transformer loosely coupled to said primary, said pr1-' mary and-secondary windings being relatively reversed, means for tuning the circuit of said'secondary for a range of wave lengths for which the anode circuitof said amplifier is aperiodic and for which said amplifier is unstable when said input and secondary circuits are tuned thereto, and loss-producing means for maintaining said amplifier stable notwithstanding tuning of said input and secondary circuits throughout said wave length range.

' 2. A tuned radio frequency amplifier system comprising a three-electrode thermionicamplifier, means for tuning the input circuit thereof, a radio frequency transformer having its primary of low number of turns in the anode circuit of said amplifier, the secondary of said transformer having a number of'turns great with respect to the number of primary turns and loosely coupled to said primary, said primary and secondary windings being so relatively. reversed that the high potential end of one of said transformer windings is adjacent the low potential end of the other for procuring low capacity coupling between said windings, a second threeelectrode thermionic device in whose input circuit said transformer secondary is in- 'cluded, means for tuning said last named input circuit for a wave length range for which the anode circuit of said amplifier is aperiodic and for which said amplifier is unstable'when said input circuits are tuned thereto, and loss-producing means in the input circuit of said amplifier for maintaining it stable notwithstanding said input circuits are tuned throughout said wave length range.

3. A tuned radio frequency amplifier system comprising a three-electrode thermionic amplifier, means for tuning the input circuit thereof, a radio frequency transformer having its primar in the output circuit of 7 said amplifier, sai primary winding having an inductance of such magnitude that said output circuit is aperiodic throughout a range of wave lengths, the secondary of said transformer loosely coupled to said primary and having a number of turns great with respect to the number of turns of said primary, said primary and secondary windings being relatively reversed, means fortuning the circuit of said secondary for said wave length range for which said .amplifier is unstable when said input and secondary circuits are tuned thereto, and loss-producing means in the input circuit of said amplifier for stabilizing it throughout said range not- 8 withstanding said input and secondarycircuits are tuned.

4. An unshielded multitube radio receiving set, the approach to each other of whose devices and connections external to the tubes effects undesired couplings, comprising a system of three-electrode thermionic devices at least one of which is a radio frequency amplifier, means for. tuning the input circuit of said amplifier, a radio frequency transform- 9 er having its'primary in the output circuit of said amplifier, said primary winding havmg an inductance of such 'magnitude that said output circuit is aperiodic throughout a range of wave lengths, the secondary of said "transformer loosely coupled to said primary,-

said primary and secondarywindings being relatively reversed, means for tuning the circuit of said secondary for said wave length range for which said .amplifier is unstable When said input and secondary-circuits are tuned thereto, the input circuit of another of said thermionic devices including said transformer secondary and said means for tuning it, and loss-producing means in the input circuits of said amplifier and said other thermionic device for efiecting stability throughout said wave length range. 5. A tuned radio frequency amplifier system comprising a three-electrode thermionic amplifier, means for tuning the input circuit thereof, a radio frequency transformer having its primary of low number of turns in the anode circuit of said amplifier, the secondary of said transformer. loosely coupled to said primary, said primary and secondary windings being relatively reversed, means for tuning the circuit of said secondary for a range of wave lengths for which said amplifier is unstable when said input and secondary circuits are tuned thereto, and means for reducing the inductance of said primary effective in the anode circuit of said amplifier and loss-producing means in the a it notwithstandilg said input and secondary spect to the number of turns of said pricircuits are tun throughout said wave mary, means for tuning the circuitof said length range. v. secondary for said wave len range for 6. A tuned radio frequency amplifier syswhich said amplifier is unsta 10 when said tern comprising a three-electrode thermionic input and seconda circuits are tuned amplifier, means for tuning the input cirthereto, and loss-pr no means in the in- 20 cuit thereof, a radio frequency transformer put circuit of said ampli er for stabilizing an inductance of such ma .output circuit is I aperiodic throughout a aflixed my signature'this 11th day of Janu- 25 having its rima Z-in the output circui of it throughout said range notwithstand' said ampli er, sai primary wmdinglhavin said input and secondary circuits are tune itude t at sai In testimony whereof I have hereunto range of wavelen hs, the secondary of said "ary, 1924. v

transformer loose 'cou led to said primary A r and. having a num r' 0 turns great with re- WILFORD C. MACFADDEN. 

